Add `force-swap` C++ source
Add `force-swap` C++ source

This is to deal with an issue where Chromium doesn't appear to allow its
memory to be (easily?) swapped.  So, I'm consistently hitting OOM
conditions even though I have a ton of free swap space.  This utility
will allocate however much memory you tell it to via CLI args, then
exit.  Forcing something other than Chromium to chew up memory seems to
allow some memory to be pushed into swap.

Example usage:

    ## allocate 500 MiB of memory
    $ force-swap 500M

    ## allocate as much memory as is considered "available", plus 500M
    $ awk '/MemAvail/ {print $2 "K 500M"}' /proc/meminfo |
      xargs force-swap

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